A system is disclosed in the U.S. patent application Ser. No. 431,649 filed on Jan. 8, 1974 wherein logic means are used to select and release stitch information stored in memory means in timed relation with the operation of a sewing machine. Digital information from the memory means is converted to positional analog signals which control closed loop servo means including moving coil linear actuators directly controlling the position of conventional stitch forming instrumentalities of a sewing machine in the formation of ornamental patterns.
In this prior art system no means was disclosed for adjusting the feed pattern for ornamental variation. In addition, in this prior art system, feed balance, for instance in a buttonhole, to have the appearance of one leg of a buttonhole generated during forward feed conform to the appearance of the other leg of the buttonhole generated during reverse feed, was achieved by a variable balance control voltage which decreased forward feed when increasing reverse feed and vice versa. Thus with the prior art system any adjustment of feed balance would affect the density of both legs of a buttonhole simultaneously but would not necessarily be optimized insofar as the desired stitch density for each leg of the buttonhole was concerned.
In this prior art system, bight adjustment was achieved by a scaling resistor which was found to have an adverse loading effect on the circuit, changing circuit parameters which influenced linearity.
What is required is a means of providing for feed pattern variation, a means to individually control forward and reverse feed to obtain for example an optimum buttonhole that would have a balanced appearance, and a means for obtaining bight adjustment which would not suffer from the above noted drawbacks.